To be used for verification of driver implementations. Note that
the skb path is gone from the series, but I'm still keeping the
implementation for any possible future work.

$ xdp_hw_metadata <ifname>

On the other machine:

$ echo -n xdp | nc -u -q1 <target> 9091 # for AF_XDP
$ echo -n skb | nc -u -q1 <target> 9092 # for skb

Sample output:

  # xdp
  xsk_ring_cons__peek: 1
  0x19f9090: rx_desc[0]->addr=100000000008000 addr=8100 comp_addr=8000
  rx_timestamp_supported: 1
  rx_timestamp: 1667850075063948829
  0x19f9090: complete idx=8 addr=8000

  # skb
  found skb hwtstamp = 1668314052.854274681

Decoding:
  # xdp
  rx_timestamp=1667850075.063948829

  $ date -d @1667850075
  Mon Nov  7 11:41:15 AM PST 2022
  $ date
  Mon Nov  7 11:42:05 AM PST 2022

  # skb
  $ date -d @1668314052
  Sat Nov 12 08:34:12 PM PST 2022
  $ date
  Sat Nov 12 08:37:06 PM PST 2022

Cc: John Fastabend <john.fastabend@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Anatoly Burakov <anatoly.burakov@intel.com>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>
Cc: Magnus Karlsson <magnus.karlsson@gmail.com>
Cc: Maryam Tahhan <mtahhan@redhat.com>
Cc: xdp-hints@xdp-project.net
Cc: netdev@vger.kernel.org
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20230119221536.3349901-18-sdf@google.comSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>